Hitachi 8450H/R - Manual (Page 65)

Ch 3: Installing Optional Devices
Hitachi PC VisionBase 8450H/R Server 61
When the capacity of the hard disks for disk array A differs from that for disk array B
Depending on the capacity of the reserve disk, the hot spare might not function.
Hot spare changes with the capacity of the reserve disk in the following way.
It is assumed that the capacity of disk array A is less than that of disk array B (A-x < B-x).
•
When the capacity of the reserve disk is the same as that of B-x:
The reserve disk serves as a hot spare in both disk arrays A and B.
For hot spare in disk array A (1 and 3 in “When there are two or more disk arrays at RAID level 1 or 5” on
page 60), the capacity of the reserve disk is larger than hard disk A-x used in disk array A, therefore the hard
disk after the rebuilding will contain unused (unusable and useless) areas.
•
The capacity of the reserve disk is the same as that of A-x:
The reserve disk serves as a hot spare in disk array A but not in disk array B.
Because the capacity of the reserve disk is less than the hard disk B-x, the data cannot be restored onto the disk.
For that reason, disk array B remains in degraded mode.
To prevent these, you need to use the same capacity for both disk arrays or provide a reserve disk for each disk array.
The priority for reserve disks used when a failure occurs is as follows (1 takes priority over 2):
1. Reserve disk with the same capacity as the failed disk
2. Reserve disk whose SCSI ID is smaller